During steelmaking, it is necessary to determine the amount of specific elements which influence the properties. Once this analysis has been made, the composition can be adjusted to meet the particular specification. In order to carry out the analysis, a sample of the steel is obtained using one of the many available techniques resulting in a solid form, usually disc-like. This sample may be analyzed by several procedures known to the art.
For rapid analysis, samples are usually prepared in the solid form by grinding a surface to a clean and flat condition and then analyzing the ground surface by a technique such as x-ray fluorescence (XRF) or optical emission (OE). In the case of certain elements which exist in steel, in both solid solution and compound form, the metallurgically-significant component is usually an acid-soluble component (hydrochloric, nitric or sulfuric acid are frequently used for solubilization). Aluminum is an example of such an element. Amongst other uses, aluminum is used for deoxidation of steel and the acid soluble aluminum content of steel provides a measure of the degree of deoxidation.
The prior art techniques of XRF and OE analysis suffer from the disadvantage that fundamentally they do not distinguish between the acid-soluble and acid-insoluble forms of elements and in fact they tend to respond more to the acid-insoluble form. In practice, therefore, supplementary methods for the determination of the acid-soluble fraction are necessary.
An alternative procedure which has been adopted is the determination of elements from an aqueous solution of sample. This procedure requires that fine drillings or millings from the steel sample are covered with strong acid and heated at close to boiling temperature for about 40 minutes until the steel sample is completely dissolved. Generally, the solution then must be brought to standard volume and acidity prior to analysis by a variety of techniques. The disadvantage of this method is that it generally takes too long for the results of analysis (by any method) to be available soon enough to be of value for process control, i.e., the adjusting of the composition of the steel to a specified range. Any attempt to shorten the time of dissolution by increasing the temperature and/or concentration of the acid may result in the partial dissolution of previously insoluble compounds. For example, in the case of the aluminum determination, the metallurgically-significant aluminum would be overestimated.